Afaik. RA and psoriasis are probably caused by a malfunction of genes which regulate IL-23 production. IL-23 is required for Th17 cells to survive. Th17 cells produce a lot of things which result in inflammation and since TNF-α is a key mediator in inflammation and break down of joints, reducing the amount of available TNF-α reduces the inflammation.
(Th17 cells produce IL-17, IL-21, IL-22, IL-6 and TNF-α. Th17 cells are playing against Treg cells, which try to protect self cells. IL-17 promote osteoclastogenesis, and osteoclasts break down bone. According to several Wikipedia articles IL-17 induces the production of other cytokines such as IL-6, IL-1β, TNF-α. IL-21 is required for sustained CD8+ T cell effector activity. IL-22 is a mediator of cellular inflammatory responses. IL-6 modulates the resistance of T cells against apoptosis, induces activation of T helper cells and promotes osteoclastogenesis. TNF-α is an endogenous pyrogen which is able to induce fever, apoptotic cell death, cachexia, inflammation and inhibits tumorigenesis and viral replication. IL-1β is a mediator of the inflammatory response, and it is involved in the regulation of apoptosis as well.)
Adalimumab is an immunoglobulin, which binds to TNF-α, and so it prevents it from binding to TNF-α receptors and causing inflammation. After it is bound to its target you cannot reuse it, that's why you need daily doses of it. It is degraded by liver and kidney cells, and probably by phagocytes.
There are other TNF-α blocking pharmaceuticals. There are IL-23 inhibitors, one of which is ustekinumab. It is an immunoglobulin too and it is used for treating psoriasis. For, RA it is currently under clinical trial, but I guess it will work for RA as well. There is an IL-23 inhibitor which is not an immunoglobulin and can be taken orally, called apilimod. Sadly it failed the clinical trials; it had only a mild effect. It probably does not reach the inflammation in sufficient amounts. Maybe one day there will be an effective delivery method and thus a drug which can be taken orally.
There are alternative natural therapies: TNF-α inhibitors which you can take orally, for example γ-linolenic acid, ω−3 fatty acids, chondroitin sulfate, etc... These can be useful for mild cases of RA. Probably fever therapy works for mild cases as well. Afaik. cryotherapy has nice results in treating RA and its positive effect lasts much longer than the effects of any drugs, so if you aren't afraid of cold, that is a nice alternative therapy as well.