Several categories of medication can interfere with a perm, either by changing your hair’s internal structure, thinning it to the point where it can’t hold a curl, or altering its texture so the chemical solution doesn’t process evenly. The most common culprits are hormonal medications, blood pressure drugs, anti-seizure medications, thyroid drugs, cholesterol-lowering medications, and chemotherapy. If you’re on any of these and planning a perm, understanding why they cause problems can save you time, money, and potential hair damage.
How Medications Interfere With Perms
A perm works by breaking and reforming the protein bonds inside each hair strand. For this to succeed, the hair needs a relatively consistent internal structure from root to tip. Medications that circulate through your bloodstream reach the hair follicle and get incorporated into the growing strand itself. This can change the hair’s porosity (how easily it absorbs chemicals), its thickness, and the arrangement of its protein bonds. When these properties are uneven, the perm solution penetrates some sections faster than others, resulting in a curl that’s patchy, limp, or drops out entirely within days.
Some medications also trigger a type of hair shedding called telogen effluvium, where a large number of follicles shift into their resting phase at once. The hair that regrows afterward is often finer and structurally different from the hair it replaced. A strand that’s partway old growth and partway new, thinner growth won’t respond uniformly to perm solution.
Hormonal Medications
Oral contraceptives are among the most frequently reported medications that affect perm results. Birth control pills can trigger diffuse hair shedding that begins three to five months after starting the medication. This shedding usually stops on its own after a few weeks, but the regrowth may differ in texture and diameter from the rest of your hair. A more significant form of thinning, androgenetic alopecia, can develop after about six months of use, particularly with pills whose progestin component is derived from nortestosterone. This type of thinning produces finer, weaker strands that are prone to over-processing during a perm.
Hormone replacement therapy and thyroid medications can cause similar texture shifts. Thyroid drugs are specifically listed alongside oral contraceptives as causes of telogen effluvium. If your thyroid medication dose has recently changed, your hair may be growing in at a different rate or thickness than the existing length, creating an uneven canvas for a perm.
Blood Pressure Medications
Beta-blockers, a common class of blood pressure and heart rate medication, are a recognized cause of telogen effluvium. Propranolol, one of the most widely prescribed beta-blockers, has been documented in case reports as a trigger for hair loss. ACE inhibitors like captopril also appear on the list of drugs associated with this type of shedding. The resulting mix of older, thicker hair and newer, finer regrowth creates inconsistent porosity along the strand, which is the main reason perms fail to hold evenly.
Diuretics, another staple of blood pressure management, can contribute to the problem indirectly. They alter your body’s fluid and mineral balance, and since hair needs adequate minerals like zinc and iron for normal growth, prolonged use may subtly change what your follicles produce.
Anti-Seizure Medications
Anti-seizure drugs have some of the most dramatic and well-documented effects on hair texture. Valproate (commonly prescribed under brand names like Depakote) is a standout example. Research has shown that increasing the dose of valproate can cause noticeable changes in hair curliness, and when the dose is lowered, the curliness disappears but thinning may persist. Multiple case studies have documented that hair regrowing after valproate-related shedding comes back curly, even in people whose hair was previously straight.
This matters for perms in two ways. First, if your hair’s natural curl pattern is already being altered by the medication, adding a chemical curl on top of that is unpredictable. Second, valproate-related thinning weakens the strand, raising the risk of breakage during processing. Other anti-seizure medications, including topiramate and carbamazepine, have also been linked to hair changes, though the texture effects are less pronounced than with valproate.
Chemotherapy and Post-Chemo Hair
Chemotherapy is in a category of its own. These drugs are designed to target rapidly dividing cells, and hair follicle cells are among the fastest-dividing in the body. During treatment, most patients experience significant hair loss. When hair regrows afterward, it frequently comes back with a completely different texture, thickness, or even color. Straight hair may return curly (a phenomenon known as “chemo curls”), and the strands are often finer and more fragile than before.
Residual chemotherapy agents can linger in the hair follicles and continue to alter how hair grows for months after treatment ends. Experts at MD Anderson Cancer Center advise skipping harsh chemical treatments, including dyes and bleaches, on post-chemo hair. Perms fall squarely into this category. The structural unpredictability of post-chemo hair makes it nearly impossible for perm solution to process consistently, and the fragility of the new growth raises the risk of severe breakage. Most stylists recommend waiting at least a year after your last chemotherapy session, and ideally until your natural texture has fully stabilized, before considering any chemical service.
Other Medications That Affect Results
Several other drug classes can quietly undermine a perm:
- Cholesterol-lowering drugs (hypolipidemic agents): These are recognized triggers of telogen effluvium and can thin the hair enough to affect how it holds a curl.
- Oral retinoids (like isotretinoin for acne): Retinoids change the skin and its appendages, including hair. They can make hair drier, more brittle, and less elastic, all of which interfere with perm processing.
- Amphetamines and stimulant medications: Listed among drugs that cause telogen effluvium, these can produce the same uneven growth patterns that lead to inconsistent curl.
- Antidepressants and mood stabilizers: Lithium and certain SSRIs have been associated with hair texture changes and shedding, though the effects vary widely between individuals.
Why a Strand Test Matters More Than Usual
If you’re taking any medication and want a perm, a strand test is the single most useful precaution. This involves applying the perm solution to a small, inconspicuous section of hair and processing it fully before committing to the whole head. It reveals whether the solution is absorbing evenly, whether the curl is forming properly, and whether the hair can withstand the chemical stress without breaking.
There is currently no standardized laboratory method to objectively screen hair for medication-related structural changes before a chemical service. The strand test is the practical substitute, and any experienced stylist will insist on one if you mention you’re on medication. Be upfront about every medication you take, including supplements and topical treatments. What seems unrelated to your hair may be the exact reason a perm won’t hold.
How Long Medication Effects Linger
Hair grows roughly half an inch per month. A medication that affected your hair follicle six months ago produced a section of altered hair that’s now about three inches from your scalp. Below that point, the strand may be structurally normal. Above it, newer growth may also be normal if you’ve stopped the medication. But that three-inch band in the middle still carries the changes.
This means that even after stopping a medication, its effects remain in the existing hair until that hair is cut off or grows out completely. For shoulder-length hair, that can take two to three years. If you recently discontinued a problem medication, you’ll get more predictable perm results by waiting until enough new, unaffected growth has replaced the older hair, or by working with your stylist to focus the perm on sections that grew in after the medication change.