alterations. Synergistic responses are a complicating factor in environmental modeling. Pest synergy Pest synergy would occur in a biological host organism population, where, for example, the introduction of parasite A may cause 10% fatalities, and parasite B may also cause 10% loss. When both parasites are present, the losses would normally be expected to total less than 20%, yet, in some cases, losses are significantly greater. In such cases, it is said that the parasites in combination have a synergistic effect. Drug synergy Mechanisms that may be involved in the development of synergistic effects include: Effect on the same cellular system (e.g. two different antibiotics like a penicillin and an aminoglycoside; penicillins damage the cell wall of gram-positive bacteria and improve the penetration of aminoglycosides). Bioavailability (e.g. ayahuasca (or pharmahuasca) consists of DMT combined with MAOIs that interfere with the action of the MAO enzyme and stop the breakdown of chemical compounds such as DMT). Reduced risk for substance abuse (e.g. lisdexamfetamine, which is a combination of the amino acid L-lysine, attached to dextroamphetamine, may have a lower liability for abuse as a recreational drug) Increased potency (e.g. as with other NSAIDs, combinations of aspirin and caffeine provide slightly greater pain relief than aspirin alone.). Prevention or delay of degradation in the body (e.g. the antibiotic Ciprofloxacin inhibits the metabolism of Theophylline). Slowdown of excretion (e.g. Probenecid delays the renal excretion of Penicillin and thus prolongs its effect). Anticounteractive action: for example, the effect of oxaliplatin and irinotecan. Oxaliplatin intercalates DNA, thereby preventing the cell from replicating DNA. Irinotecan inhibits topoisomerase 1, consequently the cytostatic effect is increased. Effect on the same receptor but different sites (e.g. the coadministration of benzodiazepines and barbiturates, both act by enhancing the action of GABA on GABAA receptors, but benzodiazepines increase the frequency of channel opening, whilst barbiturates increase the channel closing time, making these two drugs dramatically enhance GABAergic neurotransmission). More mechanisms are described in an exhaustive 2009 review. Toxicological synergy Toxicological synergy is of concern to the public and regulatory agencies because chemicals individually considered safe might pose unacceptable health or ecological risk in combination. Articles in scientific and lay journals include many definitions of chemical or toxicological synergy, often vague or in conflict with each other. Because toxic interactions are defined relative to the expectation under "no interaction", a determination of synergy (or antagonism) depends on what is meant by "no