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Men and women show different patterns of drug abuse, with women becoming addicted to some substances much more quickly. Now a study in rats has found that sex hormones can reduce opioid abuse.

From studies of other drugs, such as cocaine and alcohol, we know that women are less likely to use these substances than men, but become addicted faster when they do. “There are a lot of data to indicate that women transition from that initial use to having a substance-use disorder much more rapidly,” says , a psychologist at Davidson College, North Carolina.

Once addicted, women also seem to have .

Tracking drug use throughout women’s menstrual cycles suggests that both these differences could be shaped by hormones – with more intense cravings and greater euphoria at particular times in the cycle, says Smith.

Craving crash

Now Smith’s team has investigated the effects of hormones on opioid addiction in rats. Their findings suggest that hormones such as oestrogen and progesterone may help women to kick the habit.

The researchers allowed female rats to self-administer heroin, and measured how much they chose to take at different times in their oestrous cycle – a regular sequence of hormone fluctuations similar to those seen in the menstrual cycle in women.

They found that the rats massively reduced their heroin use during the phase of their cycle at which oestrogen levels are high and progesterone levels are about to peak. “Every single female showed this effect,” says Smith. “It didn’t matter if they were a high heroin user or a low heroin user: they still showed a decrease relative to what they used during other phases of their cycle.”

“I think it’s a really exciting study,” says , a psychologist at the University of Michigan in Ann Arbor – although she adds that “there are still a lot of questions to be answered”.

Picking the moment

One question is which particular hormones might be reducing drug cravings – oestrogen and progesterone may each separately have an effect, or they may be working together.

Other evidence points the finger specifically at progesterone. Some studies have shown that women given progesterone supplements report fewer positive feelings from both and . The hormone is being tested in clinical trials as a treatment aid for nicotine addiction.

These findings could point to new ways to tackle the opioid epidemic in the US. Between 1999 and 2014, the number of deaths from opioid overdose there quadrupled. Although more men than women die from drug overdoses, the proportion of women dying from opioids has risen more steeply. In 2010, the number of women in the US who died from opioid painkillers was – compared with a rise among men by a factor of 3.6.

Becker suggests that it may be possible to use the menstrual cycle to boost a woman’s chances of beating addiction. Because cravings and drug enjoyment seem to decrease at certain times, giving up a drug at a strategic point in a woman’s cycle may increase her chances of quitting. “It’s letting your own hormones be the guide,” says Becker.

Many women already artificially boost their levels of progesterone and oestrogen by taking contraceptive pills or hormone replacement therapy. It is, however, unclear what affect this has on addiction because little information has been collected on it – a problem that Smith is now contemplating.

Journal reference: Psychopharmacology, DOI:

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