Is it possible for hair loss to return after reducing the amount of Minoxidil usage from twice to once a day?

Thank you for your question. You are asking if you can reduce application of minoxidil 5% to once a day instead of twice a day, and if doing so will cause hair loss.
I can help guide with you with this, even without a physical exam and more details about your hair loss situation. I’m Dr. Amiya Prasad. I’m a Board Certified Cosmetic Surgeon and Fellowship Trained Oculoplastic Surgeon. I’ve been in practice in Manhattan and Long Island for over 20 years. I’m the founder of TrichoStem Hair Regeneration Centers, which employ a non-surgical pattern hair loss treatment for men and women using PRP and extracellular matrix since 2011, which pioneered a new classification of hair loss treatment.
You can reduce the use of minoxidil to once a day instead of twice a day. I do recommend to patients who use minoxidil to do so once a day. However, you need to realize the limitations of minoxidil.
Although the exact mechanism of minoxidil is not known, it appears to delay the normal shedding phase of hair, and prolongs the growth cycle so you have more hair on your head at a given time. Minoxidil won't thicken your hair, or stop hair loss. You need to maintain use daily to sustain these effects, or you can get a sudden hair shed after you stop using minoxidil.
Even if minoxidil has worked for you recently, it is quite common for the effects of minoxidil to wane over time, even if you use it daily at once or twice a day.
I see from your profile that you are 20-years-old. If you are experiencing male pattern hair loss at this age, you are highly DHT-sensitive. All men have DHT in their system, but men with pattern hair loss are genetically predisposed to have DHT-sensitive hair follicles. If you experience pattern hair loss in your 20s, you are much more DHT-sensitive to a man who starts losing hair in his 40s. Minoxidil doesn’t treat DHT, so you should consider a DHT-blocker like finasteride. I do find finasteride works better than minoxidil in treating male pattern hair loss as it blocks the formation of DHT by inhibiting the enzyme 5-alpha reductase, which converts testosterone to dihydrotestosterone (DHT). Finasteride can slow hair thinning and hair loss progression, and effects can be sustained as long as you take it daily.
If you want to stimulate hair growth, and thicken thinning hair, you can consider a treatment like our Hair Regeneration treatment that uses platelet-rich plasma (PRP) and extracellular matrix by ACell. This treatment uses a wound healing mechanism to restart a healthy hair growth cycle, so thinning hair can be induced to shed, and thicker hair grows in its place. Dormant hair follicles that have not been growing can be stimulated to regrow hair. Finasteride would still be prescribed to a man your age along with this treatment as it’s not a DHT-blocker. Using finasteride can extend the benefit of the treatment. Many male patients can get 3-5 years of benefit from a single Hair Regeneration treatment, but younger male patients with high DHT-sensitivity may get 1-3 years of benefit, depending on whether they take finasteride, and their level of DHT-sensitivity. We treat patients from all over the world every day with this treatment, and over 99% of patients, both men and women, are seeing visible results of increased hair coverage and density.
I recommend you go ahead with minoxidil applied once day, but realize the decrease in its effectiveness is not because you use it once a day, but because it really is a limited treatment for hair loss. Meet with a doctor for a finasteride prescription, and consider other proven options for managing your hair loss. I hope you found this information helpful. Thank you for your question.

Minoxidil response is dose-dependent. For this reason, the company recommends twice a day usage of minoxidil in men and once a day for women. To enhance the response, use a  .25 mm microneedle roller prior to application. Decreasing from twice a day to once a day may affect your results.

Certainly it’s possible to have hair loss when minoxidil is reduced. When one is using one half the amount, the dermal papillae deep under the scalp are receiving one half the message. For minoxidil repsonders, the result is often hair loss.