Brand-name drugs:
A drug sold by a pharmaceutical company under a specific name or trademark and is protected by a patent. One of the most common examples is “Panadol”, the chemical name/ active pharmaceutical ingredient of which is “Paracetamol”.
Generic drugs:
When the patent of a drug has expired, other pharmaceutical companies can manufacture generic drugs which consist of the same Active Pharmaceutical Ingredient as the brand-name drug.
Similarity:
The “Active Pharmaceutical Ingredient” of both brand-name and generic drugs are the same.
Difference:
Excipients (i.e. ingredients other than Active Pharmaceutical Ingredient, e.g. bulking agents, binder, flavour) of generic drugs can differ from that of brand-name drugs. Although some people may be allergic to the excipients, it is rare to encounter allergic reactions to them as commonly used excipients have undergone multiple safety research and have a long history of safety on human health.
If you never tried the active pharmaceutical ingredient before, the probability of having allergic reactions are similar for both brand name and generic drugs.