We usually view side effects as a bad thing, but sometimes they point the way to a whole new use for a drug.
"We think of...drugs as being specific to [a] task," says Harvard University medical historian Dr. Jeremy Greene. In fact, he says, "drugs are very complex objects."
As research and development costs have climbed, drug companies are more interested than ever in finding ways to repurpose their products. Often they seek to simply market an existing drug for a new condition, but in some cases they give the drug a whole new name and face. Here are eight drugs that lead double lives.
Prozac and Sarafem
When Eli Lilly's patent on Prozac (fluoxetine) expired in 2001, the company saw sales of the blockbuster drug plummet as the market opened up to competition from cheaper generic versions. In what some experts saw as a move to stem losses, Lilly began marketing fluoxetine for premenstrual dysphoric disorder, a severe form of PMS.
With the new use came a new brand: Sarafem. Pink-and-purple capsules in sunflower-bedecked packaging replaced the gender-neutral green and white of Prozac. A Lilly rep said the makeover helped give women "a treatment with its own identity," but some women were reportedly "shocked and angry" when they discovered they were effectively taking Prozac.
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Viagra and Revatio
While studying a drug for heart-related chest pain in the 1990s, Pfizer researchers discovered that men who took it experienced a surprising side effect: erections. The drug proved ineffective for chest pain, but Viagra was born.
Pfizer later explored other uses for the drug, which relaxes blood vessels, and in 2005 the Food and Drug Administration (FDA) approved it for pulmonary hypertension, under the brand name Revatio.
The drugs are identical, but taking Revatio rather than Viagra may spare pulmonary hypertension patients some embarrassment, Greene says. "There is a benefit to having a brand name that is not Viagra."
Few drugs have a more tragic history than thalidomide. In the 1950s, doctors began prescribing it to pregnant women for insomnia and nausea, but it was pulled from the market in 1961 after it was shown to cause stunted limbs and other birth defects.
A decade later, a doctor giving thalidomide to leprosy patients as a sedative noticed that it helped clear their skin lesions. In 1998, the FDA approved the drug for leprosy, but with unprecedented restrictions—like women taking it must agree not to become pregnant.
Celgene, the drug's makers, chose a name, Thalomid, that signals the drug's potential toxicity—"a remarkable rebranding strategy that meets head-on the historical baggage," Greene says.
Propecia and Proscar
Two unwelcome signs of aging for many men—male pattern baldness and an enlarged prostate—are both fueled by high levels of a type of testosterone known as dihydrotestosterone (DHT).
They are also both treated with the same DHT-reducing drug, finasteride, though it goes by different brand names: Proscar for enlarged prostate, and Propecia for hair loss. (Both are available as generics.)
"It helps you think, 'It's not that my doctor is giving me a drug that as a side effect makes you grow hair... He's giving me a drug specific for hair loss,'" Greene says.
In the 1950s Tofranil (imipramine) became the first antidepressant to enter the market. It belongs to a class of drugs called tricyclics that block norepinephrine and other brain chemicals involved in mood.
Shortly after, a psychologist realized the drug could reduce bedwetting in children, probably because it relaxes the bladder as a side effect. In 1973, the FDA approved Tofranil for that purpose in children 6 years and older.
Tofranil is infrequently prescribed for bedwetting now (due to side effects and the risk of accidental overdose), but it continues to be used as an antidepressant.
Wellbutrin and Zyban
In 1997, the FDA approved Zyban (buproprion), the first prescription drug intended to help smokers kick the habit. Zyban may have been a first, but it contained the exact same active ingredient as the antidepressant Wellbutrin, approved 12 years earlier. The two drugs come in identical purple pills.
Experts still aren't sure why an antidepressant also aids smoking cessation, but it could be that the drug causes a surge in mood-altering brain chemicals that mimics the effects of smoking cigarettes.
Amphetamine was a "drug looking for a disease," wrote Nicolas Rasmussen, in his book On Speed. Although today amphetamines are most commonly prescribed for attention deficit hyperactivity disorder (ADHD), since their discovery in 1929 they have been used for a laundry list of conditions, including asthma, depression, congestion, fatigue, and weight loss.
Abuse and concerns about addiction led to restrictions on these drugs in the 1970s and their decline from use. But amphetamines like Dexosyn (methamphetamine) are still prescribed for ADHD, as well as for weight loss in obese people.
Eli Lilly scientists set out to make a better Prozac and came up with Cymbalta (duloxetine). The drug ramps up levels of two neurotransmitters, serotonin and norepinephrine, that regulate mood and pain, whereas Prozac affects only serotonin.
Cymbalta hit the market in 2004, but like many antidepressants, its use did not stop there. The FDA has since approved it for anxiety, fibromyalgia, lower back pain, and osteoarthritis—leading one observer to call it the Swiss Army knife of drugs.
The drug is effective against all these conditions because pain and mood are so closely related, Lilly has said.