Can heat waves affect how well the pill works?

By Lauren Wilkin

A pharmacist is warning people who take the contraceptive pill that the fifth U.K. heat wave might make it less effective.

"Most medicines have specific storage conditions, and many of these medications should be kept below 25 degrees," said pharmacist Ana Carolina Goncalves.

Ana says this is because heat gradually speeds up the natural processes that cause a medicine to break down over time.

And for the contraceptive pill, this can have huge consequences.

"Many combined contraceptive pills — pills containing estrogen and progestogen — need to be stored below 25 degrees, while some other contraceptive pills need to be stored below 30 degrees.

"Some also need to be kept in their original packaging to protect them from light and moisture," Ana, who leads the team at online pharmacy Pharmica.

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"The active ingredient can lose its potency faster than it would if the medicine were kept in the conditions it was designed for," she said.

"Heat can also affect the tablet itself, including its coating, which can change how it dissolves and releases the medicine once taken. Moisture can also further accelerate this process."

And while there's not one single temperature where the contraceptive pill can suddenly become ineffective, Ana says its prolonged exposure that's a cause for concern.

"One of the highest risk situations is leaving medication in a parked car, in direct sunlight, in very hot luggage or frequently storing it somewhere warm and humid — such as a bathroom," Ana added.

So, with the U.K. experiencing its fifth heat wave this week, it's possible that where you've been storing your contraceptive pill over the summer could have impacted how effective the medication is.

"The concern with the contraceptive pill is whether that heat has affected the hormones or the way the tablet releases them, which can mean that there is no longer a guarantee that it will deliver the full intended dose each day to help consistently prevent pregnancy," added Ana.

"If you think your contraceptive pill has been exposed to significant heat, check the storage instructions for your particular medication and speak to a pharmacist if you are unsure," she said.

"A pharmacist can advise whether the pack should be replaced and whether missed-pill guidance or temporary additional contraception may be advised to prevent unplanned pregnancy."