The medicine is made from proteins and other substances produced by the body.
It's a liquid that's given as a drip or injection pen.
A biosimilar is a newer version of the original biological drug. It works in the same way.
Biosimilar medicines generally cost less than the "original brand" biological medicine, but they're just as safe and effective.
Switching patients from the original biological medicine to a biosimilar could save the NHS hundreds of millions of pounds.
And you shouldn't notice any difference – your body should respond in the same way to the newer version of the medicine.
Biosimilars are thoroughly tested in clinical trials to show they work just as well and are just as safe as the original biological medicine.
To be used in the UK, biosimilars must be approved and licensed in the same way as all medicines.
No. Generics are exact copies of the original medicine – for example, a supermarket-brand ibuprofen is the generic version or copy of Nurofen.
Biosimilars aren't generics because they aren't completely identical to the original medicine. But they're just as safe and effective.
Adalimumab is a biological medicine used to treat inflammatory conditions, such as Crohn's disease, psoriasis and rheumatoid arthritis.
The brand name of the original drug is Humira.
If you have been taking adalimumab (Humira) and your hospital decides to start using biosimilars, you should receive a letter explaining this.
It should give details of who you can contact if you have any questions.
You should be offered a conversation with your doctor or specialist nurse before you're prescribed a biosimilar.
Any decision to switch to a biosimilar will take into account your needs and preferences, as well as the available clinical evidence.
Together with your doctor or nurse, you can agree on the best medicine for you. In some cases this may mean continuing with Humira and not switching.