Generic vs Branded Medicines in India: What Actually Changes in the Drug When You Switch

Every branded drug and its generic version must contain the same active pharmaceutical ingredient at the same dosage. That is not a marketing claim, it is a legal requirement under India's Drugs and Cosmetics Act, enforced by the Central Drugs Standard Control Organisation (CDSCO). When your chemist hands you a strip of metformin 500 mg from an Indian generic manufacturer instead of the original branded version, the metformin molecule is chemically identical.
What differs is everything around it: the binders, fillers, coatings, colorants, and preservatives that make up the inactive portion of the tablet. These excipients affect how quickly the tablet dissolves, how it feels going down, and occasionally how your gut responds to it. For most people on most drugs, this difference is clinically invisible. For a small subset, it is not.
Before a generic drug is approved in India, the manufacturer must demonstrate bioequivalence, proof that the generic delivers the active ingredient into the bloodstream at a rate and extent that falls within 80 to 125% of the branded original. This is the global standard set by the WHO and adopted by CDSCO. The 80 to 125% window sounds wide, but regulators and pharmacologists consider it clinically acceptable for most drug classes because the human body's own absorption varies by a similar margin day to day.
The drugs where this margin matters most are narrow therapeutic index (NTI) drugs, medicines where a small shift in blood concentration can tip from therapeutic to toxic, or from effective to useless. Warfarin, lithium, phenytoin, levothyroxine, and digoxin fall into this category. A 2017 study published in the journal Therapeutic Drug Monitoring reviewed substitution outcomes for NTI drugs and found that patients switched without clinical monitoring showed measurably different plasma levels compared to those maintained on the branded version. Indian cardiologists and neurologists routinely advise against unsupervised switching for these specific molecules. For antibiotics, antacids, antihistamines, and most common painkillers, the substitution concern essentially disappears.

India's Pradhan Mantri Bhartiya Janaushadhi Pariyojana (PMBJP) scheme runs over 10,000 Jan Aushadhi Kendras across the country selling generic medicines at prices 50 to 90% lower than branded equivalents. The Bureau of Pharma PSUs of India (BPPI), which runs the scheme, sources from manufacturers who must clear CDSCO quality standards. A 2022 analysis by the Indian Journal of Medical Research found no statistically significant difference in therapeutic outcomes between Jan Aushadhi generics and branded counterparts across a sample of common chronic-disease drugs including metformin, amlodipine, and atorvastatin.
The price gap is not a quality signal. It reflects the absence of marketing costs, brand royalties, and the research and development expenditure that the originator company recouped during the patent period. Once a patent expires, any manufacturer who can demonstrate bioequivalence and pass quality inspection can produce and sell the molecule. The savings are structural, not a trade-off.

Three situations warrant a direct discussion before you swap strips at the pharmacy.
First: NTI drugs listed above. If you are on warfarin for a heart valve or phenytoin for epilepsy, do not switch without telling your neurologist or cardiologist. They may want a blood level check after the transition.

Second: extended-release formulations. A branded extended-release tablet and its generic version may use different polymer matrices to control drug release over 12 or 24 hours. The total drug delivered may be bioequivalent, but the release curve can differ, relevant for drugs like metoprolol XL or metformin ER, where the peak-to-trough ratio affects side effects.
Third: known excipient sensitivities. Lactose intolerance, for example, is relevant because many tablet formulations use lactose as a filler. If you switched generics and developed new gastrointestinal symptoms, the excipient list on the package insert is worth checking before assuming the drug itself is the problem.
Every tablet strip sold in India must carry the generic name (International Non-proprietary Name) prominently, the manufacturer's name, the batch number, and the expiry date. CDSCO mandates this. If a chemist substitutes a branded prescription with a generic, they are legally required to dispense the same molecule at the same dosage, not a different drug. The confusion that patients sometimes experience comes from unfamiliar brand names on the strip, not from actual changes to the drug inside.
Checking the INN on the strip takes ten seconds. Metformin is metformin whether it comes in a white strip from a Mumbai manufacturer or a blister pack from a Hyderabad plant. The dosage printed on the strip, 500 mg, 1000 mg, is the number that matters clinically. If those match your prescription, the substitution is legally and pharmacologically sound.
The real variable in a generic switch is not the molecule but the manufacturing quality of the specific producer, and that is true of branded drugs too. A branded tablet from a plant that failed a CDSCO inspection is less safe than a generic from a plant that passed. The brand name is not a quality guarantee. The CDSCO approval and the manufacturer's compliance record are.