Weight Loss Drugs & Medicines | Triage Thoughts Ep. 255

Prefer to listen? Listen on Spotify.

Why we are talking about drugs at all

In the previous episode we worked through supplementation for fat loss and gestured towards a handful of compounds that sat awkwardly on the border between supplements and medications. This is the follow-up. The medications and drugs covered here are not the kind you pick up over the counter or order from your usual supplement website. Most of them require a prescription, some sit firmly in bodybuilding circles, and some live in both worlds.

Two things to flag at the start. The first is that we are not recommending any of these as a first move. We are walking through them because understanding what they actually do tells you something important about how weight loss works at all. Importantly, even the most powerful weight loss drug ultimately has its effect through energy balance. Calories in, calories out still explains the mechanism of every single one of them. They simply change which lever you are pulling.

The second is the moralising problem that hangs over this whole conversation. There is a tendency to treat fat loss as a pure willpower test and to view anyone who uses medication as having taken a shortcut. We think that framing is unhelpful and a bit incoherent. Drugs and discipline are not opposites; they sit comfortably together. For some people, particularly at the more extreme end of obesity, medication may be the piece that lets the rest of the work even become possible. Even so, baseline habits still come first. Good nutrition patterns, training, sleep, stress management. No drug substitutes for those, and we will come back to that point at the end.

Stimulants: clenbuterol and the wider category

The stimulant that comes up most often in physique and bodybuilding circles is clenbuterol. It is a beta-2 adrenergic agonist, which means it acts on receptors that sit within the sympathetic nervous system, the branch of the nervous system that puts the body into fight or flight mode. Take clenbuterol and you put yourself into that “go” state for an extended stretch of time. The person on it will be jittery, sweatier than normal, possibly anxious, with a noticeably higher heart rate.

Mechanistically, you are ramping the resting metabolism up. The figure usually quoted is around a 20% increase in resting energy expenditure, sometimes more. If maintenance is 2,000 calories a day, an extra 10 to 20% is 200 to 400 calories of additional turnover at rest. So even with intake unchanged you would expect a deeper deficit. There may also be some appetite-blunting effect, though that is not the most consistent finding. The dominant effect is the metabolic ramp-up.

Beta-2 adrenergic receptors are not confined to fat tissue. They are dispersed throughout the body, including in skeletal muscle, which is one reason bodybuilders are drawn to clenbuterol. There are suggestions of an effect on muscle retention or even hypertrophy on top of the fat loss. In practice it is hard to tease apart, because almost nobody uses clenbuterol on its own; it sits inside a stack with testosterone and other anabolic drugs.

The downside is significant. If you turn the sympathetic side up and never let the parasympathetic side bring the system back to baseline, things go wrong. Higher heart rate, higher blood pressure, the risk of cardiac arrhythmias. Clenbuterol is also cardiotoxic, and cardiomyocytes are not the kind of cell that regenerates well, so any damage there tends to stay with you. A single tablet has been suggested to be enough to cause some heart damage. Therefore, this is not a drug we are pointing anyone towards.

Within the wider stimulant category sit drugs like Adderall, Modafinil and Ritalin, the so-called “smart drugs”. They are not prescribed for weight loss, but in practice many people on them notice they move around more, fidget more, and feel less hungry. Modafinil in particular seems to interact with hunger-relevant signalling, including orexin. We would not classify them as fat loss drugs, but it would be dishonest to pretend they have no effect in that direction. Caffeine sits at the milder end of the same family. Illicit stimulants like cocaine, MDMA and methamphetamine sit at the far end, and the fact that heavy users tend not to be carrying much body fat tells its own story.

Metabolic drugs: DNP and metformin

DNP, or dinitrophenol, is the metabolic drug that appears in bodybuilding contexts and almost nowhere else legitimate. Mechanistically it works at the electron transport chain, the final stretch of the metabolic pathway that turns the energy in food into ATP. DNP partially uncouples that process, so the energy that should have ended up as ATP is instead released as heat. Metabolic rate goes up because the cell is wasting energy.

The obvious problem is what happens when you increase thermogenesis too aggressively. You can quite literally cook yourself from the inside out. There is no clean antidote, and although risk is dose-dependent and people apparently are experimenting with smaller doses again, it is not a drug we are recommending. On top of the thermogenic risk, DNP is not made in any pharmacy. Whatever capsule someone is holding was put together by a lad in a bathtub somewhere, and the dose on the label is whatever they wrote on it.

Metformin sits in a very different place. It is a genuinely useful medication, prescribed routinely for type 2 diabetes, gestational diabetes and PCOS, among other things. Weight loss is a secondary effect rather than its primary purpose. The classical mechanisms include improved insulin sensitivity and reduced hepatic glucose output. More recently there is interest in central effects, with metformin appearing to act on areas in the brain that regulate appetite. That is a recurring theme across this whole conversation: drugs that look like they are doing something peripheral often turn out to do at least some of their work centrally.

Importantly, metformin works in part through the AMPK pathway, which sits in opposition to mTOR. Since mTOR signalling is part of how muscle is built, that makes metformin an awkward fit if your goal involves gaining or holding onto muscle. We would not be putting our hat on it as a fat loss tool, but we can see why people slot it in for nutrient partitioning reasons. There may also be some effect on exercise performance worth keeping in mind.

Hormones: testosterone, thyroid and growth hormone

A handful of hormones get listed alongside weight loss drugs because they alter how the body composes itself, even though pure fat loss is rarely the only reason anyone takes them.

Testosterone, in someone genuinely deficient, can change the picture dramatically. The person who was lethargic, low in mood and uninterested in training may suddenly find they have the energy and drive to actually do the things that lead to fat loss. Beyond that, higher testosterone tends to push nutrient partitioning towards lean mass: in a surplus, more of the gain is muscle; in a deficit, more of the loss is fat. However, people are not generally taking anabolic steroids to lose fat in isolation. The muscle-building and muscle-retention effect is usually the point.

Thyroid hormones get used heavily in bodybuilding competition prep, and the picture is genuinely similar to clenbuterol. Thyroid receptors are scattered throughout the body, and ramping thyroid hormone up ramps the whole system up. Heart rate climbs, blood pressure climbs, sweatiness and jitteriness appear, and energy expenditure increases. The same side effect profile follows, including the risk of arrhythmias such as atrial fibrillation, which is observed clinically in hyperthyroid states. Correcting a genuine hypothyroid picture is a different matter and likely to help.

Growth hormone is the odd one out. It is a strange hormone with effects that depend heavily on pulsatility, and having too much produces different outcomes than having a physiologically normal amount. Bodybuilders continue to use it, but the trial evidence for growth hormone as a weight loss drug on its own is not particularly convincing. Correcting an actual deficiency is one thing; adding it on top of normal levels and expecting fat to fall off is something else. There may be a role around morning fasted exercise, where lipolysis effects could help with stubborn areas, and there may be synergy with testosterone for muscle retention. As a standalone fat loss intervention, we are not impressed.

Orlistat: blocking fat absorption at the gut

Orlistat, sold as Xenical or Alli, takes a more mechanical route. It binds to lipases in the gut, the enzymes that break triglycerides down into the free fatty acids the body can actually absorb. With the lipases blocked, the triglycerides pass through and are excreted. The usual figure is around a 30% reduction in fat absorption. On a 100 g per day fat intake, that is roughly 30 g of fat not absorbed, which at nine calories per gram works out to about 270 calories effectively leaving the diet.

The side effects are exactly what you would predict. The fat that is not absorbed has to go somewhere, so steatorrhoea and looser stools are common. This is where doctors and bodybuilders weigh risk very differently. A bodybuilder will tolerate a fast heart rate, raised blood pressure and long-term cardiovascular risk without much complaint, but find the bathroom side of orlistat unacceptable. A doctor will happily accept the bathroom side and refuse to put a patient on something that raises cardiovascular risk. Same underlying biology, very different risk thresholds.

GLP-1 agonists: changing the appetite signal itself

The drug class that has shifted the conversation most in recent years is the GLP-1 agonists. GLP-1 stands for glucagon-like peptide-1, a hormone the body already produces. An agonist binds to the same receptor and produces the same kind of effect.

These drugs act on the gut, on the brain stem and to some extent on the pancreas. The two most clinically prominent are liraglutide, sold as Victoza or Saxenda, and semaglutide, sold as Ozempic or Wegovy. Semaglutide is the more recent and effective of the two and is the one that ended up everywhere in the press.

What they do is attenuate hunger and reduce the brain’s activation in response to food. This matters because people with obesity tend to be more sensitive to food cues and less likely to feel satisfied after a meal. That is a real, observable physiological difference, not a moral failing. The GLP-1 agonists intervene exactly at that point, allowing the person to regulate intake in a way they could not before. The experience, anecdotally, is not that you feel a drug working; it is that you simply do not feel as hungry. That is a very different sort of intervention to a stimulant where you can feel the system being pushed.

Side effects are mostly gastrointestinal, the standard nausea and looser stools that crop up with anything acting on the gut, and overall the profile is well tolerated. The other thing that stands out, and it is unusual for a weight loss intervention, is that the weight loss appears to be maintained rather than rebounding the moment the trial ends. Some obesity doctors have also used these drugs in the post-weight-loss phase to manage the insatiable hunger that often appears once someone has lost a large amount of weight and that otherwise drives the regain. We can also see plausible applications for people on the disordered eating spectrum who struggle with binge eating, and there is growing interest in bodybuilding circles, where shorter-acting versions allow appetite to be blunted without losing the ability to eat enough to hold muscle.

Naltrexone with bupropion: dampening the food reward

The last drug worth covering is a combination of naltrexone and bupropion. Naltrexone on its own is an opioid receptor antagonist. Opioids like heroin or OxyContin produce a strong reward and euphoria, and naltrexone has the opposite effect at the same receptors, dampening reward signalling. Applied to food, that means the anticipation of eating, the craving, and the satisfaction after the meal all become a little less rewarding.

Bupropion is a dopamine and norepinephrine reuptake inhibitor with an appetite-suppressing effect of its own. Put the two together and you get appetite suppression alongside a dampening of how rewarding food itself feels. Both effects are central, in the brain, rather than peripheral. The overall result is reduced energy intake.

The pattern across all of these drugs

If you look across the whole list, every drug here works on one of two levers: energy in, or energy out. Stimulants and DNP push energy expenditure up. Hormones can tilt nutrient partitioning and indirectly support more activity. Orlistat reduces what is effectively absorbed. The GLP-1 agonists and the naltrexone/bupropion combination reduce intake by changing hunger and food reward. Even the drugs that look like they are working peripherally often turn out to be working centrally as well.

That is why understanding these drugs is useful even if you have no intention of ever taking any of them. They make the underlying levers visible. If your problem is that you cannot regulate appetite, the answer looks very different to the answer for someone whose problem is that they barely move during the day. There is no one-size-fits-all fat loss drug, because there is no one-size-fits-all fat loss problem.

Drugs do not replace the basics

We want to keep coming back to this, because it gets lost easily. None of these drugs replace baseline habits. If you are not eating reasonably, sleeping reasonably, managing stress reasonably and training, reaching for a drug to raise your energy expenditure while you skip the fifteen-minute walk is missing the forest for the trees. The drug is just nudging the same levers those habits also work on, and it is doing so with side effects attached.

However, for some people the drug really is the missing piece. The person with low testosterone who cannot find the motivation to train is in a different position to the person who has not yet tried walking each day. The person with severe obesity who cannot regulate hunger no matter how clean their diet is in a different position to someone who has not yet learned to cook. Therefore, the honest answer is that drugs do not replace the basics for most people, but they may unlock the basics for some.

The moralising knee-jerk against these medications is worth resisting. The same crowd that worries loudly about the obesity epidemic is often the loudest against the drugs that are actually moving the needle on it. If you genuinely care about health outcomes, these medications have a role. We are perfectly capable of holding two ideas at once: that hard work, discipline and good habits are central, and that for some people a medication is what makes those habits possible. The “drugs versus willpower” framing is a false choice.