According to Sarafino (1996), systematic desensitization is "a well documented, highly effective method for helping people overcome their fears,"; durable effects have been reported for up to 2 years following treatment, and generalization to other areas of emotional functioning have been reported (pp. 236-237). Spiegler & Guevremont (1998) assert: "The findings of hundreds of studies assessing the effectiveness of systematic desensitization over the past 40 years are overwhelmingly positive" (p. 220).
Systematic desensitization is often used to treat fears about concrete stimuli (e.g., spiders, heights, enclosures) and generalized social evaluative situations (e.g., interviews, exams, public performance) (Paul, 1969b). However, the range is considerably more extensive than this; interesting unusual examples of problems treated with systematic desensitization, or variations thereof, include: anger (Rimm, DeGroot, Boord, Heiman, & Dillow, 1971), asthmatic attacks (Moore, 1965), motion sickness (Saunders, 1976), insomnia and nightmares (Shorkey & Himle, 1974), problem drinking (Hedberg & Campbell, 1974), sleep walking (Meyer, 1975), stuttering (Wolpe, 1969), racial prejudice (Cotharin & Mikulas, 1975), a washing compulsion (Wolpe, 1990, pp. 324-325), chronic diarrhea (Hedberg, 1973), kleptomania (Wolpe, 1982, pp. 301-302), and sexual dysfunction (Wolpe, 1990, pp. 306-309). Given this impressive list of facts, it is not surprising that systematic desensitization is still widely practiced (Spiegler & Guevremont, 1998).
Over the years research has accumulated suggesting that in vivo desensitization can result in greater fear reduction than systematic desensitization (Sarafino, 1996). However, this claim has been questioned on the basis that these were analogue studies that used subjects with mild problems. When only clinical samples of persons with severe anxieties are considered, these differences appear to dissipate (e.g., James, 1985). Spiegler & Guevremont (1998) summarize the comparison as follows: "The safest conclusion that can be drawn about imaginal versus in vivo desensitization is that both are useful and effective procedures" (p. 254).
Other research has called into doubt whether two of the defining features of systematic desensitization, relaxation and gradual exposure to the imagined feared situation, are even necessary for the procedure's success (e.g., Kazdin & Wilcoxan, 1976; Richardson & Suinn, 1973). Such results have been interpreted in different ways. Wolpe (1982) notes that the researchers often ignored the cause of the problem, which may be either classically conditioned or cognitive in nature, as well as the severity of that problem. This oversight makes him question the meaningfulness of these studies. However, Spiegler & Guevremont (1998) are lead through their review to state that while gradual exposure and a competing response may be components that facilitate the effectiveness of systematic desensitization, its essential component is: "repeated exposure to anxiety-evoking situations without the client experiencing any negative consequences" (p. 210). Leitenberg (1976) calls systematic desensitization "no more than a method of promoting exposure to actual phobic stimuli" (p. 133). Finally, taking the middle road, Sarafino (1996) writes:
"Although there is some doubt about the importance of these features to the success of desensitization, the evidence against their use is not yet clear enough to warrant dropping them. Because relaxation exercises and full stimulus hierarchies don't seem to harm clients and may help the treatment process, it's probably best to include these features in systematic desensitization." (p. 238)