Though commonplace for many people, birth control is a complex process that requires careful follow-through.

It’s common to choose a contraceptive method based on how well it’s supposed to work. However, there are factors that can make several kinds of birth control less reliable.

Most statistics that explain effectiveness are based on perfect use, meaning the method is used exactly as directed. But it’s important to remember that most people aren’t perfect with their birth control.

A better figure may be typical use. The pill, for example, is over 99% effective when used perfectly, but that drops to 91% with typical use.

Some prescription medications may make hormonal birth control less effective. These include:

Although most antibiotics do not cause any problems with contraception, this isn’t always the case. The antibiotic rifampin reduces concentrations of estrogen in the blood.

An older studyTrusted Source that reviewed more than 20 years of data from 1975 to 1998 found that the pill isn’t a reliable form of contraception when combined with rifampin.

Natural, integrative, and herbal remedies can reduce the efficacy of some hormonal birth control methods.

St. John’s wort, for example, makes many drugs less effectiveTrusted Source, including the pill.

There are different brands of the pill, but all work on a specific schedule. Forgetting to take a dose or taking it late can mean a greater chance of pregnancy.

As an example, if you’re on progestin-only pills, you must get your dose within the same 3-hour window every day for maximum effectiveness.

The Depo-Provera shot also contains progestin. It must be administered by a healthcare professional every 12 weeks to work effectively.

The skin patch and vaginal ring also have to be changed on a regular schedule. In addition, they have to stay in place in order to properly protect against pregnancy.

Take care when opening a condom package not to tear the delicate sheath inside. If you’re using an external condom, make sure you hold the tip when putting it on to make sure air doesn’t get caught inside.

Follow instructions closely when using a diaphragm, as timing makes a difference. For example, if you put in a diaphragm longer than 2 hours before sex, the spermicide won’t work as well, and you’ll get less protection.

Some people use fertility awareness as a method of contraception. This means taking precautions when you’re most likely to get pregnant according to your menstrual cycle.

This is considered one of the least effective methods of contraception, but it works for some people. Not abstaining when you’re fertile or not wearing a condom during sex on those days reduces the effectiveness of this method.

Vasectomy is one of the most effective ways to prevent pregnancy.

But you’ll need to use an additional method of birth control for the first 3 or so months after the procedure to ensure that ejaculate is completely free of sperm.

Your healthcare professional will perform a semen analysis and let you know when your ejaculate is clear.

The lactational amenorrhoea method (LAM) can be used if you plan to nurse after giving birth. Your body will temporarily stop ovulating if you’re breastfeeding and haven’t yet menstruated after delivery.

You must breastfeed at least once every 4 hours during the day and every 6 hours at night in order to produce enough of the hormone that regulates ovulation.

There’s some evidence that obesity can reduce the effectiveness of some birth control methods, but it depends on the type.

A 2013 review of studiesTrusted Source reported that the following methods may be less effective for people with overweight or obesity:

Some evidence suggests continuous use or higher doses of the pill can increase efficacy in people with overweight or obesity.

Many birth control methods come with physical and emotional changes.

If this happens to you, you may find it helpful to talk with a healthcare professional about alternative solutions to balance your birth control needs with the side effects.

Here are some reasons to see a doctor:

  • It can be difficult to use your current method correctly: For example, you may have trouble remembering to take your pill on time.
  • You have abnormal bleeding, bloating, migraines, or mood changes. Sometimes, these are expected side effects of hormonal birth control, but they can also signal several underlying conditions.
  • You experience a low libido: Sometimes, hormonal birth control causes a reduced interest in sex. If this bothers you, you may want to change your method to something that doesn’t have this effect.

You have a number of options to help with family planning and reduce the chance of unintended pregnancy. Many of these methods are highly effective, but imperfect use of birth control can make them less so.

A number of medications, some lifestyle factors, and some medical conditions can also cause birth control to work less effectively.

Talk with a healthcare professional to find a method you can use correctly, which offers the benefits and level of protection that’s best for you.