Finasteride: when to judge the effect

Three months into treatment. You run a hand through your hair and check the crown in the lift mirror. No regrowth, no disaster either. You wonder whether it’s doing anything, or whether you just need to wait longer.

At three months, the answer is almost always: too early to tell. Finasteride works slowly, and its first effect is precisely the hardest one to see. The leaflets and dermatologists give fairly precise markers.

The timelines, document by document

The tablet leaflet states that three to six months of treatment are generally needed before shedding is seen to stabilise⁴. The NHS also says some improvement can be expected after 3 to 6 months⁶. The French Society of Dermatology allows about 3 months for an effect on shedding, often at least 6 months for regrowth, and notes that the maximum effect is usually reached after a year of regular use².

To actually judge it, dermatologists ask for more time. The European S3 guideline sets a minimum of 6 months to assess the effect on shedding, and 12 months to assess regrowth¹. The British Association of Dermatologists says continuous use for up to 14 months can be needed before a benefit is seen³.

These figures don’t contradict each other. Three to six months is when a change can begin. Six and twelve months are the points at which you can reasonably draw a conclusion.

First, the shedding slows

Finasteride blocks the conversion of testosterone into DHT, the hormone that makes follicles shrink in androgenetic alopecia². So its first expected effect is that shedding stabilises. The French Society of Dermatology reports stabilisation or improvement in nearly 90% of patients².

Regrowth, when it comes, takes longer, because it follows the pace of the hair growth cycle, which is measured in months. The spray leaflet puts it this way: lowering DHT in the scalp is thought to gradually reverse the shrinking of the follicles⁵.

If you also use minoxidil lotion, its leaflets describe heavier shedding in the first weeks: we explain it in the shedding in the first weeks of minoxidil. The differences between the two medicines are covered in how finasteride and minoxidil differ.

What the trials show

The reference figures come from two one-year trials published in 1998. Kaufman and colleagues randomised 1,553 men aged 18 to 41 to finasteride or a placebo; 1,215 continued into a second year⁷. In a 5.1 cm² area of the crown that had 876 hairs at the start, the finasteride group had 107 more hairs than the placebo group at 1 year, and 138 more at 2 years. On placebo, hair loss kept progressing⁷.

Experts also compared the participants’ photos without knowing who was taking what. It’s the measure closest to what you can do at home. According to the leaflet, 48% of treated men were rated as improved at 1 year, against 7% on placebo, and 66% against 7% at 2 years⁴.

Participants followed for five years kept an improvement compared with placebo⁸. According to the leaflet, at 5 years, hair loss had stabilised in 90% of treated men based on photos⁴.

These trials have their limits. They were run with the company that marketed the drug. They involved young men with mild to moderate hair loss, mostly at the crown. And the placebo group shrank over the years: by year 5, it had only 15 men left⁴. For a receding hairline at the temples and for advanced hair loss, efficacy has not been established⁴.

What about the spray?

There is far less data. The main trial lasted 24 weeks and randomised 458 men. In a 1 cm² area, the hair count rose by 16.3 on the spray versus 6.3 on placebo⁵. The leaflet describes the efficacy as moderate, notes that about 32% of patients on the spray left the trial early, and that participants saw no difference in their own assessment⁵. There are no data beyond 6 months. The leaflet allows 3 to 6 months before the first signs⁵.

How to judge, in practice

Shedding that stabilises looks like “nothing is changing”. That is already the expected result: without treatment, androgenetic alopecia keeps progressing, as it did in the trials’ placebo groups⁷. To see it, you need a comparison.

• Always compare with your starting photo, not last week’s. From one week to the next, nothing moves.
• Take stock at 6 months for shedding and at 12 months for regrowth, the S3 timelines¹.
• Look at the same areas: the crown and your parting, where volume is easiest to read.
• Write down how you feel. The ANSM asks for regular medical follow-up during treatment, and for stopping and seeing a doctor urgently if psychiatric symptoms such as low mood or suicidal thoughts appear⁹.

The review happens with your doctor, who decides what comes next. Bringing dated photos makes that conversation far more concrete.

What if treatment stops?

Finasteride only works while you take it². After stopping, according to the leaflet, the benefits start to fade around the 6th month and are gone within 9 to 12 months⁴. The spray leaflet gives the same timelines⁵. The BAD sums it up: hair loss restarts after stopping³.

Some side effects, on the other hand, can persist after stopping: the ANSM lists this among the risks to be aware of⁹. Minoxidil lotion has its own timelines, both in use and after stopping: they are set out in when to judge minoxidil lotion.

Your day-one photo as a reference

Everything rests on a reliable starting point. Without a day-one photo, at 6 months you are comparing your scalp to a memory, and memory is always either too kind or too worrying.

Calvap helps you take comparable photos: your previous photo appears as a ghost overlay so you can match the same angle and distance every week. Your photos line up on a timeline with your treatment journal, and you can compare your first session with month 6, then month 12, in a single swipe.