TEENAGE pregnancies have hit record lows in the Western world, largely thanks to increased use of contraceptives of all kinds. But strangely, we don鈥檛 really know what hormonal contraceptives 鈥� pills, patches and injections that contain synthetic sex hormones 鈥� are doing to the developing bodies and brains of teenage girls.
You鈥檇 be forgiven for assuming that we do. After all, the pill has been around for more than 50 years. It has been through many large trials assessing its effectiveness and safety, as have the more recent patches and rings, and the longer-lasting implants and injections.
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But those studies were done in adult women 鈥� very few have been in teenage girls. And biologically, there is a big difference.
At puberty, our bodies undergo an upheaval as our hormones go haywire. It isn鈥檛 until our 20s that things settle down and our brains and bones reach maturity.
鈥淚f a drug is going to be given to 11 and 12-year-olds, it needs to be tested in 11 and 12-year-olds,鈥� says Joe Brierley of the clinical ethics committee at Great Ormond Street Hospital in London. Legislation introduced in the US in 2003 and in Europe in 2007 was intended to make this happen but a New Scientist investigation can reveal that there is still scant data on what contraceptives actually do to developing girls. The few studies that have been done suggest that tipping the balance of oestrogen and progesterone during this time may have far-reaching effects, although there is not yet enough data to say whether we should be alarmed.
It is estimated that around a quarter of girls aged between 15 and 19 in the US are using hormonal contraceptives. Girls younger than 15 are also prescribed them, often to regulate their periods, or to help with period pain or acne. . 鈥淕irls can be prescribed contraceptives as young as 9,鈥� says Andrea Bonny of Nationwide Children鈥檚 Hospital in Columbus, Ohio.
82%: Sexually active girls aged 15-19 in the US using contraception
Source: CDC, 2006-2010
It is common practice to extrapolate results gleaned from adults in clinical trials to children. Pharmacologists use models to predict the scaled-down dose that might be appropriate for a younger person.
It is estimated that this has resulted in . The laws that came into force in 2003 and 2007 have started to take effect for many drugs, but not for birth control 鈥� the US National Institutes of 午夜福利1000集合, for example, funds a contraceptive trial network but still excludes under 18s. 鈥淚 suspect it鈥檚 political,鈥� says Bonny, who has been running her own, small-scale research projects. 鈥淣o one wants to test contraceptives in minors.鈥�
Bonny has been involved in investigating whether an injectable drug called depot medroxyprogesterone acetate (DMPA) or Depo-Provera, , causes bone loss. Bone is built up and broken down throughout life, but overall bone density increases in adolescence, stabilises in middle age, and then declines.
The bare bones
Several studies have suggested that rather than gaining bone, teenagers taking Depo-Provera experience , if they have been taking it for more than two years. Although there are , the drug now comes with a warning label in the US. There is some evidence that teens who stop having the shot , but we don鈥檛 know if they reach optimum bone density, says Bonny.
There are other potential issues. Some hormonal contraceptives cause weight gain. This might be because of the changes in hormone levels they create, says Kelly Klump at Michigan State University in East Lansing. The normal fluctuation of hormones across the menstrual cycle triggers an increased appetite before a period starts. 鈥淓ssentially what [hormonal] contraceptives do is increase this phase,鈥� says Klump. She is investigating if the drugs cause women to binge eat.
Either way, weight put on when you are young can be harder to shift further down the line. 鈥淢y suspicion is body composition changes are going to have long-term consequences for obesity and metabolism,鈥� says Bonny.
That hunch is based on what we know about how the female brain develops during puberty. The swings in oestrogen and progesterone that result in irregular periods, mood swings and acne also cause the death of brain cells. This sounds dramatic but it鈥檚 a normal developmental process known as pruning, which sculpts certain brain circuits into their adult form, including the one governing metabolism.
Hormonal contraceptives suppress the release of the body鈥檚 own versions, so teens on the pill may miss out on this roller-coaster ride. 鈥淵ou鈥檙e imposing an adult hormone regimen on someone who may not experience it for another few years,鈥� says Cheryl Sisk at Michigan State University.
This means less painful periods, but there could also be an effect on pruning. This could have consequences not only for body weight, but also for other things regulated by the sculpted brain circuits 鈥� sexual behaviour and how a person processes rewards, which is linked to substance abuse, says Sisk. 鈥淚t could have long-lasting, maybe permanent effects.鈥�
Kathryn Clancy of the University of Illinois at Urbana-Champaign says imposing adult levels of sex hormones on teenagers may disrupt the development of the body鈥檚 hormone control system, which is set during adolescence. 鈥淚f you give teenagers hormones, you鈥檙e potentially setting a different 鈥榥ormal鈥� for the ovaries,鈥� says Clancy. She suspects this may signal premature development.
But the consequences are unclear 鈥� the effects might even be beneficial for all we know. 鈥淚鈥檝e tried to research this, but what鈥檚 frustrated me is the lack of research on adolescent hormonal contraceptive use,鈥� says Clancy.
There is no doubt that hormonal contraceptives have had a massive positive impact. The fall in teen pregnancies in recent years 鈥� down 50 per cent since 1999 in the UK, and 40 per cent between 2004 and 2014 in the US 鈥� is thought to have huge implications for young women, in terms of their health, education and future financial stability 鈥� as well as those of their children. But often the choice of which contraceptive doctors should prescribe to teens comes down to which a person feels comfortable taking, or which they can be trusted to use properly. These shouldn鈥檛 be the only factors, say the researchers.
A study carried out almost 30 years ago found that women of different ethnicities . Others suggest that , especially those who are using the drugs for reasons other than safe sex.
57%: Sexually active girls aged 16-19 in the UK using contraception
Source: ONS, 2008-2009
Tweaking the ratio of hormones in a contraceptive might also make them more suitable for teens. Oestrogen helps build up bone, while progesterone breaks it down. And while oestrogen can increase the risk of blood clots, the risk from this is lower for teenagers with their youthful blood vessels than it is for adults. But without trials, there is no way of knowing what will work best.
Teenage trials
There are many reasons why companies, individuals and funding organisations are reluctant to test contraceptives in teens. Andrea Bonny, a physician in Columbus, Ohio, says she gets angry letters when she advertises for young study participants, with many writers feeling that she is encouraging teenagers to have sex. 鈥淲e are inundated with negative comments鈥�.
When children participate in clinical trials, their parents must give consent. But teenagers might not want to tell their parents they are taking contraceptives, says Dirk Mentzer, chair of the European Medicines Agency鈥檚 Paediatric Committee (PDCO), which assesses clinical trials that involve children. 鈥淭his is one reason why the PDCO is not pressing organisations to run these studies,鈥� he says.
Some countries oppose testing contraceptives in children for cultural reasons, says Mentzer. And many research ethics committees will only support a clinical trial if the outcome is likely to have a positive, measurable effect on health 鈥� something that is hard to read in a trial of contraceptives.
This article appeared in print under the headline 鈥淭he contraception deception鈥�
