“The side effects of Prozac made me think I was going insane – but that’s why I’m still taking it.”

In the six years I’ve worked for The Mail on Sunday, I’ve recovered from an eating disorder, suffered several bouts of severe anxiety, moved twice and gotten married. I’m about to get divorced now.

Still, up until the end of last year, I hadn’t taken a single day off for mental health reasons — and that had nothing to do with it.

In fact, my breakdown was caused by the pills I was taking to help me deal with the stress mentioned above.

It happened in September, two weeks after I started the antidepressant Prozac, also known by its generic name Fluoxetine.

I decided to take the drug when my anxiety symptoms—palpitations, tight chest, cramped stomach—began to make daily life difficult.

Like eight million others in the UK, I have suffered from intermittent anxiety, usually triggered by stress, for most of my 31 years. I was prescribed Prozac – one of the most commonly prescribed antidepressants – twice, during my teens and early 20s, to treat anxiety. But this last time felt a little different. Within 14 days of starting treatment I was feeling… a little off.

I was at a friend’s birthday barbecue. It was a beautiful day—warm weather, pots of dip, and three kinds of sausage—but I felt like someone had lit a fire in my chest, or imagining what it would feel like to be held at gunpoint . My body was rigid, anxious thoughts racing.

I came home afterwards and collapsed on the sofa crying and then spent two hours Googling things like ‘how do you turn your mind off?’ and ‘How do you know if you have schizophrenia?’

Even more alarmingly, I developed feelings of dissociation – a feeling that the body is separate from the mind. Basically I thought I was going crazy.

After minimal sleep, I called my MoS Health colleagues the next morning and admitted for the first time that I wasn’t feeling well.

I’m not ashamed to speak out about my mental health, but my work has always been a sanctuary of sorts from my troubled mind.

This time there was nothing I could do – write, read or understand. Information just didn’t come in.

My editor insisted that I take as much time as I needed.

What followed was a frantic call to the doctor who prescribed me a low dose of the sedative diazepam and told me to call back in a few days. “It’s very common for fluoxetine to make you feel worse at first,” he told me, “but the side effects usually wear off in a month or two.”

I could feel like this for two months? I wasn’t sure if I would make it the next day.

Given all of this, it may surprise you that today I remain a staunch advocate of Prozac and all antidepressants. I’m still on the pill.

The family doctor was right. The side effects wore off after about a month and the treatment has kept me afloat at a turbulent time in my life. But as a health journalist who’s written prolifically on the benefits of antidepressants, I was taken aback by my blip.

In November, I received a slew of reviews after writing on these pages that my childhood GP first prescribed Prozac when I was just 15 to treat severe anxiety. I’ve been accused on Twitter of recommending powerful drugs to teenagers who have a history of side effects like suicidal thoughts.

According to official guidelines, antidepressants should only be prescribed to under-18s by a psychiatrist and only in severe cases. I responded immediately, arguing that the evidence showed that, by and large, antidepressants do more good than harm — and can even be life-saving for teenagers. But had my own recent experience proved me wrong?

The most commonly prescribed antidepressants in the UK are selective serotonin reuptake inhibitors, or SSRIs.

Multiple reviews examining hundreds of studies found that, on average, about 40 to 50 percent of people with depression and anxiety who take SSRIs see an overall improvement in mental health. About half of the patients experience at least one side effect. For one in ten, these problems are so severe that they stop taking them.

Side effects vary by drug, but the most common are fatigue, nausea, dizziness, stomach upset, sexual problems, and excessive excitement/anxiety. About four percent of patients have suicidal thoughts, according to the American Medical Association.

However, there is little clear information on how long these problems have lasted. The UK medicines watchdog’s guidelines, the National Institute for Health and Care Excellence (NICE), vaguely mention that the pills should start working within four weeks, while some side effects “may persist throughout treatment”. But GPs I’ve spoken to say they’ve noticed a clear trend.

“It may take about three weeks to a month before you feel normal again,” said Dr. Ellie Cannon, GP columnist for The Mail on Sunday, who added that she’s also experienced short-lived side effects from taking SSRIs. “For the first few weeks I felt very uncomfortable and when I adjust the dose it can feel like I’m going insane.”

dr Clare Gerada, psychiatrist and President of the Royal College of GPs, said: “Patients feel absolutely worse in the first three weeks. They tend to get very severe anxiety symptoms. I sometimes prescribe a sleeping pill for the first week to help patients deal with the increasing panic at night.

“But if they stick with the antidepressants, things usually improve.”

dr Penny Ward, visiting professor of pharmaceutical medicine at King’s College London, says there are several possible explanations. “The chemical combination in some SSRIs has a knock-on effect on other connections in the brain and the rest of the body,” she says.

“SSRIs turn off the body’s ability to dampen serotonin [a neurotransmitter that carries messages between nerve cells in the brain and the rest of the body].

“This could impact the central nervous system, which controls our natural fear response, and could theoretically make anxiety worse. But once serotonin has reached a level that improves mood, the anxiety becomes less bothersome.”

Few studies monitor the duration of certain side effects, but many report that many patients stop taking the pills because of side effects and when.

In a study of more than 600 patients, only 15 percent said severe side effects caused them to stop taking the pills within the first three months, although 60 percent had severe side effects in the first week. Another US study of 400 patients found that 40 percent experienced drowsiness, 30 percent experienced sexual problems (such as erectile dysfunction), 22 percent experienced insomnia, and 19 percent experienced anxiety.

In about two-thirds of cases, symptoms were only a problem for the first two weeks.

But some SSRIs are associated with earlier side effects than others — and fluoxetine seems to be one of the worst offenders.

“I would always prefer not to prescribe fluoxetine,” says Dr. Straight. “Compared to other SSRIs, you see a lot more anxiety with it.

“You get a feeling of irritability and restlessness at first because it’s slightly stimulating.”

A number of doctors I’ve spoken to over the years have told me that patients often find that antidepressants don’t work because they stop too soon. Studies show that about 60 percent of people see benefits after three months, compared to 40 percent after one month.

The message is, if you can, try to stick with it. “Ask a loved one to watch you closely for the first few weeks,” says Dr. Canon.

And if not, try something else. In 2008, experts at Pittsburgh University found that 40 percent of a group of 334 depressed patients saw an improvement in mental health after switching SSRIs.

But doctors say these drugs aren’t the be-all and end-all. There are classes of drugs that act on different brain chemicals to improve mood and reduce anxiety.

For example, SNRIs, which affect another mood-related brain chemical called norepinephrine, may be effective in those who don’t get along with SSRIs — particularly venlafaxine. There are also older classes of antidepressants like tricyclics, including amitriptyline and nortriptyline — although these are associated with side effects like drowsiness and falls.

A 2018 review by researchers at the University of Oxford compared clinical trial dropout rates — the percentage of patients who discontinued a treatment before the trial was over — and the effectiveness of 21 different antidepressant drugs.

The winners, oddly enough, were atypical antidepressants, including agomelatine, which increases production of the hormone melatonin, mirtazapine, and a tricyclic antidepressant called clomipramine. But all the drugs studied, including SSRIs, proved to be effective.

I’ve been on Prozac for six months now, which is about the time doctors recommend stopping it once you’re feeling better. And while I’m feeling far less confused, with a challenging year ahead of me, I’d rather not risk letting my brain marinate in its natural juices.

I’m aware I could stay on them for the next two, three, even five years, but as long as I get up in the morning I honestly don’t mind.