Pills That Make Us Fat

published in the March 8, 2008 issue of New Scientist Magazine by Harvard researcher Paula J. Caplan

Walk down any street in America and you’ll see the effects of the “obesity epidemic”. Two-thirds of adults, more than 130 million people, are now considered overweight, and nearly half of these are classified as obese. Those who are overweight by 45 kilograms or more are the fastest-growing group of the overweight in the US.  Accompanying these skyrocketing figures are increases in diabetes, heart problems and deaths.

In print and on the airwaves there are numerous stories about how fast food, large portions, sedentary lifestyles and poverty are playing big parts in weight gain, while government bodies desperately throw together public health programmes to educate people about the dangers their lifestyles bring.

Yet one culprit is rarely mentioned: the broad range of psychiatric drugs that can cause substantial weight gain.  They include drugs marketed as antidepressants (such as amitriptyline, doxepin and imipramine), mood stabilisers (including lithium and valproate) and antipsychotics (including clozapine, olanzapine and chlorpromazine).

After 10 years on lithium, for example, two-thirds of patients put on around 10 kilograms.  And in December 2006, The New York Times published an article based on internal documents from the drug company Eli Lilly which indicated that it had intentionally downplayed the side effects of olanzapine, which it sells as Zyprexa.

The company’s data showed that one-third of patients who have taken the drug for a year gain at least 10 kilograms, and half of these gain at least 30 kilograms.  The mechanisms behind this weight gain appear complex and are certainly poorly understood.  Some psychiatric drugs may impair the central nervous system’s control of energy intake, leading to food cravings, whereas others, such as selective serotonin reuptake inhibitors (SSRIs), may alter a patient’s metabolic rate.

Worryingly, doctors are increasingly prescribing multiple psychiatric drugs for the same patient at the same time, even though many effects of doing so, including the effect on weight, have not been investigated.  Doctors often fail to warn patients that the drugs they prescribe may increase their appetites.

We don’t know how much these drugs are adding to Americans’ waistlines, but the number of people affected is likely to be high.  Prescriptions in the US for Zyprexa alone run into millions.  In 2004, 32.6 million Americans purchased outpatient prescriptions for antidepressants, stimulants, antipsychotics and tranquillisers, up from 21 million in 1997.  Overall, around 50 million Americans – that’s 1 in 6 of the population – currently take at least one psychotropic drug.

From a crude look at the numbers, it seems that they could potentially be causing a significant – and growing – portion of America’s obesity problem.

It seems surprising then that commentators rarely make the link between psychiatric drugs and the obesity epidemic.  For example, a report broadcast last year by the PBS TV network called Fat: What no one is telling you included a vast array of lifestyle and physiological factors that could be contributing to weight gain.  Psychiatric drugs were not mentioned.

Another factor that the media and governments have failed to publicise is that rising obesity in teenagers and even young children over the past 10 to 15 years coincides with a fivefold increase in prescriptions of antipsychotic drugs in those age groups, and that children taking these drugs are even more likely to gain weight than adults are.  We don’t know how much of this increase in obesity is due to the drugs, but shouldn’t somebody be finding out?

Though drug-induced weight gain is potentially a worldwide problem, it is a particular concern in the US because American culture is so eager to label negative feelings and problems as evidence that a person is mentally ill – and to push drugs as a supposedly quick fix.  Furthermore, doctors often fail to warn patients that the drugs they prescribe may increase their appetites, and people labelled as mentally ill often learn to attribute all their problems – including eating more – to their psychological disorder.

In a curious article last May in the American Journal of Psychiatry (vol 164, p 708), two doctors even proposed that obesity be classified as a mental illness.  One likely consequence of that would be another massive increase in the prescribing of psychotropic drugs, resulting, no doubt, in another upsurge in obesity statistics.

Recent revelations that some antidepressants may work little better than placebo in most cases (see “Mindfields: Talking down antidepressants”) make the potential scale of the side effects more worrying than ever.  Anyone taking psychiatric drugs who is concerned about weight gain and its associated ill effects should be reminded that to stop taking them suddenly – and what is gradual enough for one person may be far too sudden for another – can precipitate serious withdrawal symptoms.  But at the very least, every person considering taking these drugs needs to be able to make a fully informed decision about whether to get their prescription filled.

The government and the media must take the lead in ensuring that drug companies disclose the extent of the weight gain that their drugs cause and in educating the public about the risks.

Paula J. Caplan is a clinical and research psychologist at Harvard University and author of  “They Say You’re Crazy,”