What are collagen injections side effects?

It really depends on which collagen you get. Currently there are three commercially available forms:

Bovine (cow)
Porcine ( pig)
Cadaveric (human)

Reactions differ most notably in the ability to cause an allergic reaction with decreasing severity in the order listed above. Bovine typically requires a skin test 1 month before treatment and therefore is rarely used any longer.
Most commonly people complain about the relatively short lived results but other issues are the potential lumpiness of the product. In some situations, however, it remains an excellent product for fine lines.

Collagen injections have fallen into disfavor. Bovine (cow) collagen and human collagen are hardly used any more. Skin allergies manifested as red bumps did occur in 1 - 3 % of people with bovine collagen. Porcine (pig) collagen, manufactured as Evolence, will no longer be distributed by J and J. Injectables are mostly the hyaluronic acids such as Restylane and Juvederm, Hydrelle (hyaluronic acid premixed with anesthetic) and Radiesse.
Bruising, tenderness, lumpiness, uneveness, bluish color of the skin over a lump (unique to the hyaluronic acids) and rare vascular compression complications including scarring can occur. There are other rare risks that your doctor can discuss with you.

There are several different kinds of collagen injection fillers. The oldest collagen and the original filler was made of cow collagen and about 3% of people were allergic to it. Today, the newest collagen is called Evolence. It is derived from pig collagen and is a wonderful filler. Allergies to this are very rare. However, Evolence is manufactured by Johnson & Johnson, and they have decided not to continue distribution of this product. We believe this same product will eventually be marketed by another company.

WHY would you be getting Collagen injections when there are so much better and longer lasting fillers out there?
The label COLLAGEN refers to the original products Zyderm/Zyplast (now owned by Allergan producer of Botox, Latisse and Juvederm) which were isolated from COW COLLAGEN. They could not be used in people allergic to beef products and required at least one skin test 3-4 weeks before use. (Some used 2 skin tests because up to 4% of those who did not react to the first skin test were allergic to beef products and would react to a second test). The products were NOT cheap, were short lasting.
As far as adverse effects aside from the allergy issues, the FDA prohibited the filling of lips with Collagen ("Paris Lips") but otherwise the products had a good safety record if not an impressive durability record.
With so much better products out there, a lot of us still have unused Collagen in our refrigerators. Could you ask your ?doctor if he/she would take my Collagen off my hands? I'm ready to deal....
Peter A Aldea, MD

Collagen is a dermal (skin) filler used for minimizing wrinkles or some depressed scars.  The collagen products that were widely used (Zyderm, Zyplast, CosmoDerm, CosmoPlast) were taken off the market in 2010 since Allergan, the manufacturer/distributor, also sells the Juvederm family of injectable fillers, and these fillers last longer than collagen. The Juvederm family is made of hyaluronic acid (natural substances found in our bodies, but synthetically derived from bacteria) and have become more popular than the collagen products, not only because they last longer (6 to 12 months), but they can also be injected into deeper levels, thereby acting as "volumizers". Just as a clarification, Restylane/Perlane, are also hyaluronic acid derivatives, and plastic surgeons may have a preference of one brand over the other.

All injectables may have local tissue reactions, such as needle stick marks, pain during injection, tenderness after injection, redness, bruising and swelling.  When injecting collagen products, these side effects generally last no more than 1 hour.  HA's have more local tissue reaction, so those side effects will last longer:  My personal experience is that the Juvederm family reactions last about 4 hours, Restylane/Perlane may last for about 24 hours.  The deeper fillers (Juvederm Ultra Plus and Perlane) are more likely to have persistent swelling and possibly bruising for several days. As an aside, collagen, if derived from bovine (cow), has the potential risk of allergic reaction.

There are some longer lasting products, including ArteFill, which contains bovine collagen mixed with a bone-like derivative, synthetic polymethylmethacrylate (PMMA).  It lasts for 3 to 5 years, but a significant risk is "foreign body reaction", or lumpiness at the injection site.  It is very technique dependent and although steroid injection into the lumps may help to minimize their appearance, the usual treatment is excision (cutting them out). This is a significant side effect that warrants consideration when choosing a filler! 

Finally, there has been recent attention to unusual side effects of injectable fillers.  They include unusually severe infections and embolic reactions (particle of filler enters a blood vessel and travels distally, causing a blockage of the vessel, resulting in death of the tissue the vessel supplies).  My personal belief is that we are seeing more of these problems because 1) the availability of deeper fillers and 2) many "providers" with less than adequate training and experience are administering these fillers.