Why these two appear together
The glucosamine and MSM combination is the market standard in this category. The reasons are practical: both raw materials are widely available, well tolerated at usual amounts and easy to fit into one capsule.
Appearing together does not create a joint effect. In the EU neither substance carries an authorised health claim relating to joints or cartilage.
Two substances, two different roles
Glucosamine is an amino sugar the body also produces itself and uses in building glycosaminoglycans. In supplements it usually comes from crustacean chitin or from fermentation, supplied as sulphate or hydrochloride.
MSM is a small sulphur-containing compound. Sulphur is a building block of several amino acids. Advertising often draws a line from that chemical fact to cartilage that the evidence does not support: sulphur deficiency is not described on a normal diet.
How to judge combination products
What decides is the amount of each substance per daily serving, not the length of the ingredient list. A product with many ingredients in trace amounts is not better than one with few ingredients at a stated dose.
Check additionally whether the raw material form is named and whether a conversion to the pure active substance is given. Without those, two combination products cannot be compared.
Safety aspects of the combination
For glucosamine the described possible interaction with coumarin anticoagulants applies, as does the allergy question when the origin is crustacean. For MSM, occasional digestive complaints at the start are reported.
Reliable data for pregnancy and breastfeeding are missing for both. Anyone taking medicines regularly should clear the combination with a doctor or pharmacist first.